This invention relates to a hologram apparatus for recording and reproducing data into and from a holographic memory, and more particularly to a positioning method for a spatial light modulator and an image pickup device for positioning the spatial light modulator and the image sensor on the pixel level.
In recent years, holographic techniques have been and are being developed rapidly in order to achieve practical use of holographic memories to which attention is paid as a strong storage candidate competent with next-generation and next-next-generation optical disks. A hologram recording and reproduction system, which makes use of a hologram technique to perform recording and reproduction of a large amount of data is disclosed, for example, in “Holographic data storage”, IBM J. RES DEVELOP, Vol. 44, No. 3, May, 2000.
According to the hologram storage recording and reproduction system (hologram apparatus), a coherent laser beam is split into signal light and reference light, and the signal light is intensity modulated with recording data by a spatial light modulator (SLM). The modulated signal light is condensed on a hologram recording medium (hologram recording material). Thereupon, since also the reference light is irradiated on the hologram recording medium, the signal light and the reference light interfere with each other, and interference fringes formed by the interference are recorded as fine density patterns in the recording medium.
In order to reproduce the data recorded in the hologram recording medium, illumination reproduction light same as the reference light is introduced at an angle equal to that of the reference light to the hologram recording medium. Thereupon, the data are reproduced as diffraction light (reproduction signal light) corresponding to the interference fringes recorded in the hologram recording medium. The reproduction signal light is condensed on an image sensor such as a CCD+CMOS image sensor and retrieved as bit patterns into an image pickup device. The received light signal obtained by the image pickup device is analyzed and reproduced as data.